1. Field of the Invention
This invention relates generally to method and apparatus for processing of image data of documents or other type images wherein the image data may represent different types of images.
2. Description Relative to the Prior Art
In the use of digital copier/printers, when a document with different image types (continuous tone photographs, halftone pictures, text (gray, as well as binary)) and graphics) are used with one set of output printing algorithm at one time (error diffusion, gray level halftone screening or thresholding etc.), there can be some undesirable effects occurring. For example, if an input halftone picture is printed with a lower screen frequency halftone output (like a hard dot 150 lines/inch screen) moire pattern shows up. If a text image is printed with a halftone output, the text quality (especially gray text and smaller font size text as well) degrades due to the screening. If a more continuous tone like output algorithm (like gray level error diffusion or a partial dot higher screen gray level halftone) is used, then the granularity of the continuous tone input image suffers. Sometimes those different image types can even exist on the same page. One known solution to this problem is to provide the copier/printer or other output display device such as a CRT, etc. with a manual selection device so that the customer (either through an on-screen editing function or by use of digitizing table the operator can identify various image types on the page before processing). However, this is very tedious and is not efficient to do in a walkup environment. So it is desirable to be able to segment the input image type in real time so a more appropriate output rendering algorithm can be used for each image type.
It is also known in the prior art as exemplified by commonly assigned U.S. Pat. No. 5,471,543 to provide for automatic image type processing wherein regions of a document are determined as to image type and these determinations are based on certain criteria. These regions then are processed in accordance with such determinations. A problem associated with this region building approach is that the process of assigning pixels to regions and then building regions is relatively slow and requires that the processor buffer substantial areas of the document page during the region building process.
It is therefore an object of this invention to overcome the problems associated with the prior art automatic segmentation of image data which does not require substantial buffering of image data by the processor nor requires substantial processing time for region building determinations.